In my 90Litre community tank I have 2 long fin zebra danio along with a male betta. When the danios were introduced to the tank they tried to establish authority over the betta by fin nipping him, but he just turned around and gave them a taste of their own medicine!!! Now they all swim around peacefully. They still have the odd skirmish, but the betta gives them a good chase. Usually he just camps out in one of the comfy plants and they leave him alone.
I suppose that it would also depend on the personality of the betta/danios. I agree that the danio do like a larger tank with more swimming space - they do explore and they like open areas.